Nitazoxanide (2-(acetolyloxy)-N-(5-nitro-2-thiazolyl) benzamide) is a compound having the following structure:

The preparation and uses of this compound are disclosed, for example, in U.S. Pat. No. 3,950,351 to Rossignol.
Pharmaceutical compositions containing nitazoxanide and its metabolite, tizoxanide, were originally developed and marketed for treating intestinal parasitic infections.
Following oral administration of nitazoxanide or mixtures of nitazoxanide plus tizoxanide in humans, these compounds are partially absorbed from the intestinal tract, and nitazoxanide is rapidly hydrolyzed to form tizoxanide in plasma. Tizoxanide is glucurono-conjugated, and the drug is eliminated in urine and bile as tizoxanide or tizoxanide glucuronide. The half-life of tizoxanide in plasma is only approximately 1.5 hours.
For treating intestinal infections, pharmaceutical compositions containing nitazoxanide or mixtures of nitazoxanide and tizoxanide and a wetting agent and optionally a starch derivative have been used successfully. The use of particles of active ingredients ranging between 5 and 200 μm was shown to be important to achieving safety and efficacy. The use of a pharmaceutically acceptable acid has been shown to improve the stability of these pharmaceutical compositions. See, for example, U.S. Pat. Nos. 5,387,598; 5,968,961; and 6,117,894 to Rossignol. Tablet and suspension formulations have been shown to be equally effective for treating intestinal parasitic infections regardless of their relative bioavailability.
The absorption of nitazoxanide and nitazoxanide-tizoxanide mixtures from the intestinal tract varies significantly depending on the pharmaceutical formulation. For example, the relative bioavailability of an oral suspension has surprisingly been shown to be only 70% of that of a tablet. Systemic bioavailability of these compounds has not been of paramount importance, however, because the compounds have been used almost exclusively for treating parasites that reside in the lumen of the intestinal tract or in the intestinal mucosa.
Nitazoxanide and tizoxanide have also been shown to be active in vitro against certain DNA viruses in vitro (see, for example, U.S. Pat. Nos. 5,578,621 and 5,886,013, to Rossignol). In recent years, they were surprisingly shown to have activity against hepatitis C virus (HCV), an RNA virus, in vitro and in clinical trials (Reference pending US application, “Viral Hepatitis Treatment”). The mechanism of action of nitazoxanide and tizoxanide in inhibiting virus replication is not known, but it has been postulated to be a “cell-mediated” mechanism because of its broad spectrum antiviral activity and the inability to induce resistance.
Early clinical trials of nitazoxanide and tizoxanide in treating chronic hepatitis C were conducted using a tablet formulation developed for treatment of intestinal parasitic infections. That tablet contained 500 mg of active ingredient (99% nitazoxanide/1% tizoxanide). In patients chronically infected with HCV genotype 4, sustained virologic response (SVR) rates of 61% to 80% were achieved when the tablets were administered one tablet twice daily for 4 to 12 weeks followed by the same regimen plus standard doses of peginterferon α-2a with or without ribavirin for 36 weeks. By contrast, patients treated with the standard therapy, peginterferon α-2a plus ribavirin for 48 weeks, experienced only a 50% SVR rate.
While early trials in patients with chronic hepatitis C genotype 4 showed improved efficacy using the 500 mg tablet, a significant number of patients were not cured. Higher doses of active ingredient could not be used to improve efficacy because previous studies have shown that doses of 1000 mg twice daily are associated with a significant increase in side effects, which are primarily related to the intestinal tract (e.g., abdominal pain, diarrhea and nausea). These side effects reduce patient compliance with the treatment regimen and are particularly unacceptable for long-term treatment of patients with hepatitis C.
For treating chronic HCV infection, tizoxanide must be delivered into the bloodstream and to the infected hepatocytes. Ideally, the drug should be administered by oral route no more often that twice daily and without significant side-effects in order to maximize the adherence of patients to the treatment regimen.
The variable absorption of nitazoxanide and tizoxanide in different dosage formulations, the very short half-life of tizoxanide in plasma and side-effects associated with high doses of nitazoxanide and tizoxanide in the intestinal tract are problems that must be overcome in developing a new optimized dosage formulation for treating chronic hepatitis C. Furthermore, because the mechanism of action of nitazoxanide against HCV is unknown, it is impossible to know whether fluctuations in peak and trough concentrations at the site of infection are beneficial or detrimental to improving efficacy.
Thus, there is a need for a solid dosage formulation of nitazoxanide and/or tizoxanide with improved efficacy in treating chronic hepatitis C compared to tablets described in the prior art, and without any increase in side effects.